This invention relates to the preservation of foodstuffs which are perishable through oxidation or organic decomposition by maintaining the foodstuffs in an inert gas atmosphere and more particularly to a method of and means for preserving foodstuffs by maintaining them in a container of air at substantially atmospheric pressure from which oxygen has been removed by generating hydrogen and reacting it with such oxygen without substantial increase in the hydrogen content of the air in the container or substantial decrease in the pressure of the air in the container.
The major constituent of air is nitrogen gas (N.sub.2) which comprises over 75% of dry air at sea level, on the average, both by weight and by volume, whereas oxygen gas (O.sub.2) normally comprises over 20% of dry air, both by weight and by volume, with the balance of about 2% of dry air being composed of trace amounts of other gases. It has long been known that if the oxygen is removed from the air in a container of foodstuffs, the remaining nitrogen rich atmosphere will contribute markedly to the preservation of such foodstuffs. Thus, U.S. Pat. No. 77,768 granted to Schoonmaker in 1868 proposed to preserve grain by placing it in a substantially sealed container and providing means for circulating the air in the container through a closed system over a heated bed of oxidizable solids to remove the oxygen from the air. Similarly, U.S. Pat. No. 709,431 granted to Baker in 1902 teaches the inclusion of oxidizable solids within a substantially sealed volume containing perishable foodstuffs for the purpose of removing the oxygen from the air in such volume. According to the teaching of both patents, means are provided for maintaining atmospheric pressure within the volume or container.
However, the oxidizable solids must be periodically replaced and the effectiveness of each charge of oxidizable solids in removing the oxygen from the air in the container or volume will steadily decrease over the life thereof.
It is an object of this invention to provide a method and means for preserving perishable foodstuffs by removing the oxygen from a container of air surrounding such foodstuffs which do not involve the use of oxidizable solids and in which the rate of removal of the oxygen is solely dependent on amount of oxygen present in the air.
According to the teaching of U.S. Pat. No. 677,837 granted to Wrightnour in 1901, it was proposed to preserve perishable foodstuffs by introducing liquid air into a closed volume containing such foodstuffs and rely on the fact that nitrogen gas is given off first in the evaporation of liquid air to force out the air present in the volume and provide a nitrogen rich atmosphere in such volume. However, the charge of liquid air must be replaced before any appreciable evaporation of oxygen gas therefrom thus requiring more or less constant attendance and frequent maintenance. Similarly, U.S. Pat. Nos. 3,239,360 and 3,415,310 teach the replacement of the air in a substantially closed volume containing perishable foodstuffs with an inert gas such as nitrogen gas from a prepared source thereof.
It is another object of this invention to provide a method of and means for utilizing the nitrogen gas present in the air in a container for perishable foodstuffs as the inert gas required to preserve such foodstuffs by removing the oxygen therefrom and without adding inert gas from a prepared source other than the air.
It has been proposed in a series of patents to use various methods and means for preserving perishable foodstuffs by controlling the relative amount of oxygen and carbon dioxide present in the air in a volume containing such foodstuffs (see, for example, U.S. Pat. Nos. 2,780,923 and 3,102,777- 3,102,780). However, such methods and means have required some degradation in the foodstuffs to provide the carbon dioxide involved therein.
It is a further object of this invention to reduce toward a minimum the production of carbon dioxide by the degradation of perishable foodstuffs due to oxidation thereof and to reduce toward minimum the amount of carbon dioxide present in the air contained in a container with perishable foodstuffs.
It has heretofore been proposed to use various oxidizable gaseous or vaporous substances to remove oxygen from the air in a substantially closed volume containing perishable foodstuffs by reacting such substances with the oxygen in the air. For example. U.S. Pat. No. 2,789,059 teaches the use of substances such as water gas, methane, benzene, alcohol or other hydrocarbons including butane to react with the oxygen in the air in a volume containing perishable foodstuffs. However, the oxidation of such substances produces byproducts which may contaminate the foodstuffs to give them an undesirable taste and, in fact, the substances themselves will tend to impart an undesirable taste to the foodstuffs. In addition, it is necessary to maintain a continuous supply of such substances for use in removing the oxygen from the air.
It is yet another object of this invention to remove the oxygen from the air in a container for perishable foodstuffs by reacting it with a gaseous substance which is tasteless and which produces tasteless byproducts when oxidized.
Finally, it has been proposed heretofore, to scavenge or purge oxygen from substantially closed containers by introducing hydrogen gas into such containers. For example, in U.S. Pat. No. 3,437,428 it is proposed to add hydrogen gas from a prepared source to the air in a container and react the resultant mixture in a catalytic bed to combine the oxygen and hydrogen into water. According to U.S. Pat. No. 3,598,518, oxygen is removed from closed containers by first flushing the containers with hydrogen gas and then filling the containers with the desired inert gas. However, hydrogen is dangerous to store and use in large quantities since it is inflammable and explosive in the presence of oxygen.
It is yet another object of this invention to remove the oxygen present in the air present in a container with perishable foodstuffs by reacting such oxygen with hydrogen to produce water without increasing the hydrogen content of the air in the container and without requiring the storage or use of much more hydrogen than is required to combine with the oxygen available from the air within container.